Common sense tells us that the best way to store batteries is at room temperature and in a dry place, which is the same for both nickel-metal hydride and lithium-ion batteries. When overcharging occurs, the heat generated by the current will undoubtedly be dissipated in large quantities, causing the positive electrode electrolyte of the lithium-ion battery to react and consume the maximum capacity of the lithium-ion battery. When the heat accumulates to a certain level, events such as fire and explosion may occur.
First, a safety valve (the vent hole on top of the battery) is installed. When the internal pressure of the battery rises to a certain value, the safety valve opens automatically to ensure the safety of the battery during use.
Secondly, by selecting appropriate separator materials, when the temperature rises to a certain value, the micron-sized pores on the separator will automatically dissolve, thus preventing lithium ions from passing through and stopping the internal reaction of the battery.
Third, a switching element is used. When the temperature inside the battery rises, its resistance also rises. When the temperature is too high, the power supply will automatically stop.
Many people believe that as long as lithium-ion batteries are used correctly in our portable megaphones and other electronic products, it will be fine. However, with so many users, improper use of lithium-ion batteries is inevitable, causing unnecessary damage. Therefore, the above three protection mechanisms have been developed for lithium-ion batteries to solve the problem of over-discharge or over-charge.
Faced with such a low level of safety, mobile phone manufacturers and charger manufacturers naturally won't sit idly by. After all, they're the ones who will suffer when users experience safety issues. Therefore, there are many things to consider when charging mobile phones, especially for the now mainstream USB-based phones and chargers.
They really go to great lengths to prevent overcharging.
In fact, most mobile phones nowadays have IC protection features. The charger itself also monitors voltage and current. To protect the battery and user safety, trickle charging is often used in mobile devices.
When charging via USB, assuming no losses in the cable, the USB charging port negotiates with the phone to match the appropriate current. This ensures that the phone doesn't suffer significant current loss due to high current input. This is especially important when the battery level is low, such as around 10%.
At this point, the battery is charged most efficiently, and the current reaches its maximum. As the capacitance increases, the current required by the phone gradually decreases. When the battery is at its last 10% to 20% charge, the phone may even request a small pulse current to charge it, thus protecting the battery. This charging method is called trickle charging and is currently the mainstream charging method for mobile phones. It aims to reduce the loss of the battery's maximum capacity and extend its lifespan.
Besides overcharge protection provided by the phone battery, another way to prevent overcharge is through the charging socket. For a socket to provide overcharge protection, it must first supply a stable voltage; greater voltage fluctuations will affect the current. Especially in my country, where voltage fluctuations are frequent at night, ensuring a stable output voltage from the USB port is crucial. Generally, the voltage of a USB charging port is 5V. Some USB charging ports that can intelligently distribute current will slightly reduce the voltage when the phone battery is close to full charge, thus reducing the input current and relieving battery stress.
These methods are very effective at suppressing overcharging of mobile phones, but ultimately it is because we do not unplug the power cord after the phone has finished charging, causing the phone to repeatedly discharge and charge, which leads to a reduction in the upper limit of battery capacity.
